1. Field of the Invention
Subject matter of the invention are magnetic particles having a glass surface, and a procedure for purifying a biological material, especially nucleic acids, using glass particles in the presence of chaotropic salts. Yet another subject matter of the invention is a procedure for isolating these biological materials and a procedure for concentrating biological materials and transferring them from solutions having a high concentration of salts to solutions having a low concentration of salts.
2. Description of the Related Art.
Many biological materials, especially nucleic acids, present special challenges in terms of isolating them from their natural environment. On the one hand they are often present in very small concentrations and, on the other, they are often found in the presence of many other solid and dissolved substances that make them difficult to isolate or measure.
For this reason, many procedures and materials for isolating nucleic acids from their natural environment have been proposed in recent years. In Proc. Natl. Acad. USA 76, 615-691 (1979), for instance, a procedure for binding nucleic acids in agarose gels in the presence of sodium iodide in ground flint glass is proposed.
The purification of plasmid DNA from bacteria on glass dust in the presence of sodium perchlorate is described in Anal. Biochem. 121, 382-387 (1982).
In DE-A 37 34 442, the isolation of single-stranded M 13 phage DNA on glass fiber filters by precipitating phage particles using acetic acid and lysis of the phage particles with perchlorate is described. The nucleic acids bound to the glass fiber filters are washed and then eluted with a menthol-containing buffer in Tris/EDTA buffer.
A similar procedure for purifying DNA from lambda phages is described in Anal. Biochem. 175,196-201 (1988).
The procedure known from the prior art entails the selective binding of nucleic acids to glass surfaces in chaotropic salt solutions and separating the nucleic acids from contaminants such as agarose, proteins or cell residue. To separate the glass particles from the contaminants according to the prior art, the particles are either centrifuged or fluids are drawn through glass fiber filters. This is a limiting step, however, that prevents the procedure from being used to process large quantities of samples.
The use of magnetic particles to immobilize nucleic acids after precipitation by adding salt and ethanol is described in Anal. Biochem. 201, 166-169 (1992) and PCT GB 91/00212. In this procedure, the nucleic acids are agglutinated along with the magnetic particles. The agglutinate is separated from the original solvent by applying a magnetic field and performing a wash step. After one wash step, the nucleic acids are dissolved in a Tris buffer. This procedure has a disadvantage, however, in that the precipitation is not selective for nucleic acids. Rather, a variety of solid and dissolved substances are agglutinated as well. As a result, this procedure can not be used to remove significant quantities of any inhibitors of specific enzymatic reactions that may be present.
A porous glass in which magnetic particles are embedded is described in U.S. Pat. No. 4,233,169.
Magnetic, porous glass is also available on the market that contains magnetic particles in a porous, particular glass matrix and is covered with a layer containing streptavidin. This product can be used to isolate biological materials, e.g., proteins or nucleic acids, if they are modified in a complex preparation step so that they bind covalently to biotin.